Snake‐venom phospholipase A₂ neurotoxins

Abstract

The venoms from Crotalinae and Viperinae snakes contain only two kinds of phospholipase Az neurotoxins (p-neurotoxins) : single-chain B-neurotoxins, such as agkistrodotoxin and ammodytoxin-A, and dimeric p-neurotoxins, which, in the case of the best studied ones, crotoxin-like toxins, consist of the non-covalent association of a phospholipase A2 (CB) and a non-enzymatic chaperon (CA). Possible evolutionary relationships of these p-neurotoxins have been investigated by analyzing whether CA could behave as a chaperon toward agkistrodotoxin and ammodytoxin, as it does in the crotoxin complex.CA increased the lethal potency of agkistrodotoxin and modified its pharmacological effect on Torpedo synaptosomes. Sedimentation experiments proved that CA can form an heterocomplex with agkistrodotoxin. Agkistrodotoxin prevented the binding to CA of an anti-CA mAb which recognizes an epitope at the zone of interaction between crotoxin subunits, suggesting the association of CA and agkistrodotoxin implicated the same zone.A 10-fold molar excess of CA over ammodytoxin modified the effect of ammodytoxin on acetylcholine release but did not increase the lethal potency of ammodytoxin. Sedimentation experiments showed CA and ammodytoxin can form an heterocomplex which is less stable than CA . agkistrodotoxin. Ammodytoxin A did not compete with the anti-CA mAb.These observations are in good agreement with the sequence similarities between CB and agkistrodotoxin (80%) and ammodytoxin A (60%).Phospholipases A2 (PLA2s) are ubiquitous enzymes which catalyze the specific hydrolysis of the 2-acyl ester bond of 1,2-diacyl-

Molecular evolution and structure–function relationships of crotoxin-like and asparagine-6-containing phospholipases A2 in pit viper venoms

“…The finding that CA partially protects monomeric neurotoxins such as trimucrotoxin from binding to calmodulin ( Figure 6C) is in agreement with previous reports that addition of CA increased the neuromuscular blocking effects of trimucrotoxin [12] and agkistrodotoxin [27], but not Cvv-N6 (Table 5). This is also consistent with the result of calmodulin pull-down assay that CA could not bind or protect Cvv-N6 from calmodulin binding.…”

“…The complete amino acid sequences of these N6-PLA 2 s were predicted from the cDNA sequences and matched against the mass and N-terminal sequences of the purified PLA 2 s (Tables 1 and 2). Alignment of all the N6-PLA 2 sequences obtained from the present study and previous works [11][12][13][27][28][29][30] shows that their sequence identities are approx. 73-94 % ( Figure 4A).…”

“…CA has been known to form a complex with CB with high affinity (K d = 10 −8 -10 −9 M) [38], and prevent non-specific binding of CB [25][26][27]. CA may increase the toxicity of CB more than 30-fold and those of trimucrotoxin and agkistrodotoxin severalfold towards mouse or chick tissue [12,27].…”

“…CA may increase the toxicity of CB more than 30-fold and those of trimucrotoxin and agkistrodotoxin severalfold towards mouse or chick tissue [12,27]. CA also inhibited the in vitro enzymic activities of CB isoforms, and the inhibition was weak in the presence of deoxycholate because the anionic detergent interfered with the binding between CA and CB [41].…”

Inhibition of carrageenin‐induced rat paw oedema by crotapotin, a polypeptide complexed with phospholipase A2

“…This raises the possibility that crotapotin could interact with extracellular PLA2 generated during the inflammatory process thereby reducing the hydrolytic activity of the latter. Indeed, this type of interaction with other group II PLA2 has already been shown by Choumet et al (1993). These workers demonstrated the existence of a complex between crotapotin and the single chain PLA2, agkistrodotoxin and that the formation of this complex enhanced the biological activity of the PLA2.…”